I think the most important part will be strict rules and norms for content and code. Market will be effective only if you will be able to separate garbage from useful things. Things need to be clean even if you download and install high amount of content. I would not like to see there amateur models made using tutorials and authors that just want to make some money even without required experience.
I think there can be rule that every models will need to have LOD and good optimalization. I would not like to buy unfinished work 